chemical management of western snowberry · 6/12/1987 · chemical management with herbicide...

Chemical Management of Western Snowberry

Llewellyn L. Manske PhDRange Scientist

North Dakota State UniversityReport DREC 06-1063 Dickinson Research Extension Center

Western snowberry colonies invade andspread rapidly by means of extensive rhizomesystems in pastures managed by traditional grazingpractices that weaken the competitive abilities ofgrass plants. The aerial stem canopy cover of healthywestern snowberry colonies shades sunlight from thegrass understory, reducing the forage biomassproduction in a pasture and decreasing the livestockcarrying capacity. Chemical management withherbicide treatments can reduce or eliminate theshrubs from the grassland ecosystem and permit fullsunlight to reach the grass. Two years after shrubremoval by herbicide treatment, the grass biomassproduction can increase three to six times greater thanthe pretreatment production, depending on theprevious density of the shrubs. After three years withshrub removal, the increase in grass biomassproduction can equal the weight of the shrubs on anuntreated area. Chemical management of westernsnowberry uses herbicides that interfere with vitalphysiological processes within the plant. Herbicideactive ingredients from different chemical groupsaffect various plant processes. Effective chemicalmanagement requires an understanding of the generalproperties and characteristics of the herbicidesapproved for woody plant control or suppression ongrazingland.

Herbicide Classification

Herbicides are classified by their generalroute of entry and their method of activity in plants. The mode of entry is categorized as either foliage-active or soil-active. The type of activity iscategorized as either nonselective, with chemicalactivity on contact of any plant, or selective, withchemical translocation from entry point to site ofactivity.

Foliage-active herbicides are applieddirectly to leaves and stems of plants by spraying orwiping and usually have limited residual activity inthe soil. Contact foliage-active herbicides arenonselective and kill the plant tissue directlycontacted by the chemical. Translocated foliage-active herbicides penetrate the leaves and stems ofplants, move through the phloem vascular system, and

are translocated to the roots and other organs somedistance from the point of entry (Scifres 1980).

Soil-active herbicides are applied directly tothe soil within the vicinity of the root zone of targetplant species. Translocated soil-active herbicidesmust be moved into the soil by rainfall, absorbed bythe plant roots, and then moved upward through thexylem vascular system, which consists of nonlivingvessel cells (Scifres 1980). A few herbicides can betransported both downward through the phloem fromthe leaves and upward though the xylem from theroots. Nonselective soil-active herbicides are used insome industrial areas to remove all vegetation. Thistype of herbicide is not used on grazinglands.

Most of the herbicides labeled forrangelands and grasslands were developed for othermarkets first. Development of new herbicide activeingredients is expensive for chemical companies, andthere is a low profit potential for herbicides specificfor grazinglands. As a result, there are relatively fewchemicals available for use as woody plant control ongrazinglands. Some improvements in herbicideefficacy and reductions in application rates and intotal costs per acre have resulted from thedevelopment of synergistic mixtures of existingherbicides. One new active ingredient (aminopyralid)was developed by Dow AgroSciences in 2005. Thenew herbicide, Milestone, is labeled for control ofbroadleaf herbaceous plants in rangelands,pasturelands, and noncroplands. This herbicide canbe safely applied right up to water’s edge or in areaswith a high water table.

A list of herbicides and synergistic mixturesof herbicides used in western snowberry managementis on table 1. The herbicides are sorted by themechanisms of action; the chemical group, tradename, and production company name for eachherbicide are also included on table 1.

Herbicide Toxicity

Herbicides are intended to be toxic toundesirable plants, but they also may have varyingdegrees of toxicity to humans and other organisms. The toxicity of herbicide chemicals is measured by

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the lethal dose (LD) or lethal concentration (LC) thatkills 50% of the test animals, which are usually rats orrabbits (table 2). Toxic quantities that are ingestedorally, exposed to the dermal layer of skin, andinhaled as vapor are measured separately. The oraland dermal lethal dosages are expressed as milligrams(mg) of toxicant per kilogram (kg) of body weight(mg/kg), and the inhaled lethal concentration isexpressed as milligrams (mg) of toxicant per liter (l)of aerosol (mg/l).

Highly toxic herbicides have an LD50 of 50to 500 mg/kg for a single oral dose and an LD50 of200 to 1000 mg/kg for a single dermal dose. Moderately toxic herbicides have an LD50 of 500 to5000 mg/kg for a single oral dose and an LD50 of1000 to 2000 mg/kg for a single dermal dose. Slightly toxic herbicides have an LD50 of 5000 to15000 mg/kg for a single oral dose and an LD50 of2000 to 20000 mg/kg for a single dermal dose(Hamilton et al. 2004). None of the herbicides usedin the chemical management of western snowberryare highly toxic. The herbicides are either moderatelyor slightly toxic to humans and other mammals, andgenerally a one-time exposure results

in minimal irritation. Herbicide applicators need towear appropriate personal protective equipmentdescribed on the respective product labels.

Beef Animal Restrictions

The grazing and haying restrictions for beefanimals on grazinglands treated with herbicides usedin western snowberry management are on table 3. These herbicides are either nontoxic or have lowtoxicity to domesticated animals and have no grazingrestrictions at the application rates labeled for pastureuse. Glyphosate (Roundup) that is applied by wipertechnique at less than 3 quarts product per acrerequires seven days without livestock grazing formaximum performance of the chemical, but thechemical does not pose any toxicity problems for thelivestock. The restriction period between herbicideapplication and harvest of treated vegetation for hayranges from zero days to one year (table 3). Therestriction period required between slaughter ofanimals and their removal from herbicide treatedpastures ranges from zero days to thirty days (table3).

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Table 1. Chemical name, chemical group, trade name, and company name of herbicides used in western snowberry management.

Mechanism of ActionHerbicide Chemical Name Chemical Group Trade Name Producer Company

Name

Growth Regulates or Synthetic Auxins

2,4-D low volatile ester Phenoxy 2,4-D LVE Several

2,4-D amine Phenoxy 2,4-D A Several

dicamba Benzoic acid Banvel Micro Flo Co.

dicamba Benzoic acid Clarity BASF

dicamba + 2,4-D Benzoic acid + Phenoxy Weedmaster BASF

triclopyr Pyridine Garlon 3A Dow AgroSciences

triclopyr + 2,4-D Pyridine + Phenoxy Crossbow Dow AgroSciences

triclopyr + fluroxypyr Pyridine + Pyridine PastureGard Dow AgroSciences

picloram Picolinic acid Tordon 22K Dow AgroSciences

picloram + 2,4-D Picolinic + Phenoxy Grazon P+D Dow AgroSciences

ALS Enzyme Inhibitors

metsulfuron Sulfonylurea Ally XP Dupont

metsulfuron Sulfonylurea Cimarron Dupont

metsulfuron +chlorsulfuron Sulfonylureas Cimarron X-tra Dupont

ALS Enzyme Inhibitor + Growth Regulators

metsulfuron + dicamba + 2,4-D Sulfonylurea + Benzoic acid + Phenoxy

Cimarron Max Dupont

EPSP Synthase Inhibitor

glyphosate Aliphatic Roundup Monsanto

Photosystem II Inhibitor

tebuthiuron Amide Spike 20P Dow AgroSciences

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Table 2. Toxicological test data of herbicides used in western snowberry management.

Trade Name Chemical Name

IngestionOral LD50

(rat)(mg/kg)

SkinDermal LD50

(rabbit)(mg/kg)

InhalationVapor LC50

(rat)(mg/L-4h)

2,4-D LVE 2,4-D low volatile ester 1161 >2000 N/E

2,4-D A 2,4-D amine 837-1492 2871 N/D

Banvel dicamba 2629 >2000 >5.4

Clarity dicamba 3512 >2000 >5.3

Weedmaster dicamba + 2,4-D 1150 >2000 >20.3

Garlon 3A triclopyr 1847-2574 >5000 N/E

Crossbow triclopyr + 2,4-D 1000-2589 >5000 >5.0

PastureGard triclopyr + fluroxypyr 2389-2675 >5000 >5.6

Tordon 22K picloram >5000 >5000 >8.11

Grazon P+D picloram + 2,4-D 2598 >2000 N/E

Ally XP metsulfuron >5000 >2000 >5.3

Cimarron metsulfuron >5000 >2000 >5.3

Cimarron X-tra metsulfuron +chlorsulfuron

>5000>5000

>2000>2000

>5.3>5.9

Cimarron Max metsulfuron (ptA) +dicamba + 2,4-D (ptB)

>50001497

>2000>2000

>5.3>2.07

Roundup glyphosate >5000 >5000 2.6

Spike 20P tebuthiuron >2000 >2000 N/A

Data from Material Safety Data Sheets

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Table 3. Grazing and haying restrictions for beef animals on grazinglands treated with herbicides used in western snowberry management.

Restrictions for beef animals

Chemical Name Trade Name

Periodbeforegrazing

Periodbeforehaying

Removalbefore

slaughter

2,4-D low volatile ester 2,4-D LVE 0d 30d 3d

2,4-D amine 2,4-D A 0d 30d 3d

dicamba Banvel 0d 7d 30d

dicamba Clarity 0d 0d 30d

dicamba + 2,4-D Weedmaster 0d 37d 30d

triclopyr Garlon 3A 0d 14d 3d

triclopyr + 2,4-D Crossbow 0d 14d 3d

triclopyr + fluroxypyr PastureGard 0d 14d 3d

picloram Tordon 22K 0d 14d 3d

picloram + 2,4-D Grazon P+D 0d 30d 3d

metsulfuron Ally XP 0d 4hr 0d

metsulfuron Cimarron 0d 4hr 0d

metsulfuron + chlorsulfuron Cimarron X-tra 0d 4hr 0d

metsulfuron + dicamba + 2,4-D Cimarron Max 0d 37d 30d

glyphosate Roundup 7d 7d 0d

tebuthiuron Spike 20P 0d 1yr 0d

Data from product labels

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Herbicide Properties and Characteristics

Phenoxy Herbicides

All of the numerous formulations of 2,4-Dare phenoxy herbicides that are syntheticallyproduced growth hormones similar to auxin. Theester forms of 2,4-D are more toxic per unit of acidequivalence for most plants and do not mix withwater unless emulsified. The amine forms of 2,4-Dare generally less toxic than the ester forms, but theyhave no volatility hazard and they are directly solublein water. The exact mode of action is virtuallyimpossible to ascertain because the physiologicaleffects are so complex. The phenoxy herbicidescause changes in nitrogen metabolism, respiration,photosynthesis, and nucleic acid metabolism; theyeffect changes in the composition of carbohydrates,lipids, organic acids, ethylene alkaloids, steroids,aromatics, vitamins, pigments, minerals, hormones,nucleic acids, and enzymes; and they stimulatemeristematic activity that results in abnormalmorphological changes and twisting and curling ofstems (Scifres 1980). Phenoxy herbicides are shortlived in the environment and have limited mobility,with movement through soil to groundwater unlikely. Phenoxy herbicides are rapidly decomposed by soilmicrobes, sunlight, and plant metabolism (Hamiltonet al. 2004).

2,4-D low volatile ester (LVE) ismanufactured by several companies for control ofannual, biennial, and perennial weeds and brush onpastures, rangeland, CRP acres, and noncropland. This herbicide is toxic to aquatic invertebrates andcannot be applied directly to water. This productcontains 66.2% 2,4-D, with the acid equivalent (ae)of 3.8 lbs per gallon. Nonionic surfactants may beadded to the spray mixture, and their use isrecommended for application to woody plants onpasture and rangeland. The label rates for control orsuppression of buckbrush on grazingland are 2.14 to2.85 lb ae 2,4-D (2.25 to 3.0 qt product) per acre. Repeat treatments may be required (data fromproduct label).

2,4-D amine is manufactured by severalcompanies for control of annual, biennial, andperennial weeds and brush on pastures, rangeland,CRP acres, and noncropland. This herbicide is toxicto aquatic invertebrates and cannot be applied directlyto water. This product contains 47.3% 2,4-D, withthe acid equivalent (ae) of 3.8 lbs per gallon. Nonionic surfactants may be added to the spraymixture, and their use is recommended for applicationto woody plants on pasture and rangeland. The label

rate for control or suppression of buckbrush ongrazingland is 1.9 lb ae 2,4-D (2 qt product) per acre. Repeat treatments may be required (data fromproduct label).

Benzoic Acid Herbicides

Dicamba is a broad spectrum benzoic acidherbicide. The exact mode of action has not beendefined; however, the complex reactions in plants tobenzoic acid phytotoxicity are similar to those causedby the phenoxy herbicides. Benzoic acid herbicidesalso disrupt the physiological processes of nucleicacid metabolism and photosynthesis (Scifres 1980). Dicamba is degraded by microbial activity andremains only a short time in the environment. Inwarm, moist soil, dicamba has a half-life of <14 days,and in native grasses and litter, the half-life is only 3to 4 weeks (Hamilton et al. 2004).

Banvel is a water-soluble liquidmanufactured for Micro Flo Co. for control of annual,biennial, and perennial broadleaf weeds and woodybrush and vine species on pasture, hay, rangeland,noncropland, and CRP acres. This herbicide cannotbe applied directly to water. This product contains48.2% dicamba, with the acid equivalent (ae) of 4.0lbs per gallon. Agriculturally approved adjuvants,emulsifiers, surfactants, wetting agents, drift controlagents, and penetrants may be used for wetting,penetration, or drift control. The specific applicationrates of this herbicide that control western snowberryhave not been determined through research. Thelabel rates for control or suppression of woodyspecies on grazingland are 0.5 to 1.0 lb ae dicamba (1pt to 1 qt product) per acre broadcast applied and nomore than 2.0 lb ae dicamba (2 qt product) per acreas a spot treatment. The amount of herbicide appliedcannot exceed a total of 2.0 lb ae dicamba (2 qtproduct) per treated acre per growing season (datafrom product label).

Clarity is a water-soluble liquidmanufactured by BASF for control of annual,biennial, and perennial broadleaf weeds and woodybrush and vine species on CRP acres, noncropland,pasture, and rangeland. This herbicide cannot beapplied directly to water. This product contains56.8% dicamba, with the acid equivalent (ae) of 4.0lbs per gallon. Agriculturally approved nonionicsurfactants and crop oil concentrates may be added tospray mixtures. The specific application rates of thisherbicide that control western snowberry have notbeen determined through research. The label rates forcontrol or suppression of woody species ongrazingland are 0.5 to 1.0 lb ae dicamba (1 pt to 1 qt

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product) per acre broadcast applied and no more than2.0 lb ae dicamba (2 qt product) per acre as a spottreatment. The amount of herbicide applied cannotexceed a total of 2.0 lb ae dicamba (2 qt product) pertreated acre during a growing season (data fromproduct label).

Weedmaster is a selective postemergencemixture manufactured by BASF for control of annual,biennial, and perennial weeds and brush on CRPacres, noncropland, grass (hay or silage), pastures,and rangeland. This herbicide is toxic to aquaticinvertebrates and cannot be applied directly to water. This product contains 12.4% dicamba and 35.7% 2,4-D, with the acid equivalents (ae) of 1.0 lb dicambaper gallon and 2.87 lb 2,4-D per gallon. Nonionicsurfactants may be added to the spray mixture. Thespecific application rates of this herbicide that controlwestern snowberry have not been determined throughresearch. The label rates for control or suppression ofwoody species on grazingland are no more than 0.5 lbae dicamba and 1.44 lb ae 2,4-D (2 qt product) peracre broadcast applied and 0.5 to 1.0 lb ae dicambaand 1.44 to 2.87 lb ae 2,4-D (2 to 4 qt product) peracre as a spot treatment. The amount of herbicideapplied cannot exceed a total of 1.0 lb ae dicambaand 2.87 lb ae 2,4-D (4 qt product) per treated acreduring a growing season (data from product label2004).

Pyridine Herbicides

Triclopyr and fluroxypyr are pyridineherbicides. The complex reactions in plants topyridine phototoxicity are similar to those caused bythe phenoxy herbicides (Scifres 1980). Breakdown ofpyridine herbicides occurs in soil by leaching,photodegradation, and microbial activity, with therate of breakdown related to temperature. Movementthrough soil to groundwater is unlikely, and mobilityin runoff water is limited (Hamilton et al. 2004).

Garlon 3A is a speciality herbicide manufactured by Dow AgroSciences for control ofwoody plants, broadleaf weeds, vines, and deciduoustrees on noncropland and forests, including grazingareas. Use within production forests may includeherbicide applications to control target vegetation inand around standing water sites if no more than one-third to one-half of the water area is in a singletreatment. This product contains 44.4% triclopyr,with the acid equivalent (ae) of 3.0 lbs per gallon. Addition of an agriculturally labeled nonionicsurfactant to the spray mixture is recommended for allfoliar applications. The specific application rates ofthis herbicide that control western snowberry have

not been determined through research. The labelrates for treatment of woody plants on range andpasture sites where grazing is allowed are no morethan 2.0 lb ae triclopyr (two-thirds gallon product)per acre per growing season. Spot treatments ofproblem plants in grazed areas may be conductedwhen the treated sites compose no more than 10% ofthe total grazable area (data from product label 2003).

Crossbow is a speciality herbicide mixturemanufactured by Dow AgroSciences for control oftrees and brush, and annual, biennial, and perennialbroadleaf weeds on rangeland, permanent grasspastures, CRP acres, and noncropland. This productmay not be applied to forage that is to be cut and soldfor commercial purposes. This herbicide is toxic tofish and cannot be applied directly to water. Thisproduct contains 16.5% triclopyr BEE and 34.4%2,4-D LVE, with the acid equivalents (ae) of 1.0 lbtriclopyr per gallon and 2.0 lb 2,4-D per gallon. Continuous agitation of spray mixture is necessarybecause this herbicide forms an emulsion in water,not a solution, and separation may occur. Thespecific application rates of this herbicide that controlwestern snowberry have not been determined throughresearch. The label instructions and rates forsuppression of buckbrush on grazingland are to usethe 1.5% mixture (2.0 fl oz product per gallon ofwater) at 1.0 lb ae triclopyr and 2.0 lb ae 2,4-D (4 qtproduct) per acre. The amount of herbicide appliedcannot exceed a total of 1.0 lb ae triclopyr and 2.0 lbae 2,4-D (4 qt product) per acre per growing season. Hard to control species will require retreatment or adouble rate application. Spot treatments of problemplants in grazed areas may be conducted when thetreated sites compose no more than 10% of the totalgrazable area (data from product label 2005).

PastureGard is a herbicide mixturemanufactured by Dow AgroSciences for control ofbroadleaf herbaceous and woody plants in rangeland,permanent pastures, and noncropland. This herbicideis toxic to fish and cannot be applied directly towater. This product contains 25.0% triclopyr and8.6% fluroxypyr, with the acid equivalents (ae) of 1.5lb triclopyr and 0.5 lb fluroxypyr per gallon. Using anonionic surfactant may improve weed control. Thespecific application rates of this herbicide that controlwestern snowberry have not been determined throughresearch. The label rates for the control of woodyplants on grazingland are 0.56 lb to 1.5 lb ae triclopyrand 0.19 lb to 0.5 lb ae fluroxypyr (3 pt to 8 ptproduct) per acre broadcast applied. The amount ofherbicide applied cannot exceed a total of 1.5 lb aetriclopyr and 0.5 lb ae fluroxypyr (4 qt product) per

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treated acre per growing season (data from productlabel 2005).

Picolinic Acid Herbicides

Picloram is a picolinic acid herbicide thatinterferes with a multitude of vital processes andenzyme systems, disrupts nucleic acid metabolism,and stimulates abnormal meristematic activity thatcauses twisted stems and death of growing points(Scifres 1980). Picloram is an effective broadspectrum herbicide because it is readily absorbedboth by upper and lower leaf surfaces and by theroots, and it can move through either the phloem orthe xylem vascular systems. Picloram degradesrapidly by sunlight; however, degradation by soilmicroorganisms and plant metabolism is slow andmay require 3 to 6 months, with the half-lifedepending on rainfall and soil temperature. Thepersistence is longer in cooler climates, and some ofthe chemical may leach to lower soil depths(Hamilton et al. 2004).

Tordon 22K is a restricted use pesticidemanufactured by Dow AgroSciences for control of broadleaf weeds and woody plants and vines onrangeland, permanent grass pastures, CRP acres, andnoncropland. This herbicide cannot be applieddirectly to water. This product contains 24.4%picloram, with the acid equivalent (ae) of 2.0 lbs pergallon. The addition of a surfactant may improveefficacy during drought conditions or when plantsurfaces are dusty. The specific application rates ofthis herbicide that control western snowberry havenot been determined through research. The labelrates for the control of woody species on grazinglandare 0.5 lb to 1.0 lb ae picloram (1 qt to 2 qt product)per acre broadcast applied and no more than 1.0 lb aepicloram (2 qt product) per acre as a spot treatment. The amount of herbicide applied cannot exceed atotal of 1.0 lb ae picloram (2 qt product) per acre pergrowing season (data from product label 2005).

Grazon P+D is a restricted use pesticidemixture manufactured by Dow AgroSciences forcontrol of annual and perennial broadleaf weeds andwoody plants on CRP acres, rangeland, andpermanent grass pastures. This herbicide cannot beapplied directly to water. This product contains10.2% picloram and 39.6% 2,4-D amine, with theacid equivalents (ae) of 0.54 lb picloram per gallonand 2.0 lbs 2,4-D per gallon. Grazon P+D is a water-soluble liquid, and a nonionic surfactant may be usedto provide more complete wetting and coverage of thefoliage. The specific application rates of thisherbicide that control western snowberry have not

been determined through research. The label rates forthe control of woody species on grazingland are 0.14lb to 0.54 lb ae picloram and 0.5 lb to 2.0 lb ae 2,4-D(1 qt to 4 qt product) per acre. The amount ofherbicide applied cannot exceed a total of 0.54 lb aepicloram and 2.0 lb ae 2,4-D (4 qt product) per acreper growing season (data from product label 2002).

Sulfonylurea Herbicides

Metsulfuron and chlorsulfuron aresulfonylurea herbicides that disrupt enzyme systems,rapidly inhibiting growth; within 1 to 3 weeks themeristemetic tissue at the growing points dies(product label). Sulfonylurea herbicides aremoderately persistent in soil, with a typical half-lifeof 30 days. Degradation by soil microbes is generallyslow, with increased rates at high soil temperaturesand high soil moisture. Nonmicrobial hydrolysisdegrades the herbicides slowly at high pH andrelatively rapidly at lower pH (Hamilton et al. 2004).

Ally XP is manufactured by DuPont forcontrol of broadleaf weeds and woody species onpastures and rangeland. This herbicide cannot beapplied directly to water. This dry flowable productcontains 60% metsulfuron methyl. Use of a nonionicsurfactant is recommended. The label rates forsuppression of western snowberry are 0.2 to 0.3 ozproduct per acre broadcast applied and 1.0 oz productper 100 gallons of water as a spot treatment. Theamount of herbicide applied cannot exceed a total of0.75 oz product per acre (data from product label2001).

Cimarron is manufactured by DuPont forcontrol or suppression of broadleaf weeds and brushon pastures, rangeland, CRP, and noncropland. Thisherbicide cannot be applied directly to bodies ofwater. This dry flowable product contains 60%metsulfuron methyl. A nonionic surfactant should beused. The label rates for control or suppression ofwestern snowberry are 0.12 oz to 0.60 ozmetsulfuron (0.2 to 1.0 oz product) per acre broadcastapplied and 0.60 oz metsulfuron (1.0 oz product) per100 gallons of water as a spot treatment. The degreeof suppression varies with the rate used, the size ofthe weeds, and the environmental conditionsfollowing treatment. The amount of herbicideapplied cannot exceed a total of 1.0 oz metsulfuron(1.67 oz product) per acre per year (data fromproduct label 2005).

Cimarron X-tra is a herbicide mixturemanufactured by DuPont for control of weeds andbrush on pastures, rangeland, CRP acres with

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established grasses, and noncropland. This herbicidecannot be applied directly to water. A 20-ounce unitpack of this product contains 30.0% metsulfuron and37.5% chlorsulfuron in separate compartments. Anonionic surfactant must be used in the spray mixture. The specific application rates of this herbicide thatcontrol western snowberry have not been determinedthrough research. The label instructions and rates forcontrol or suppression of western snowberry ongrazingland are to use Rate I–0.15 oz metsulfuronand 0.19 oz chlorsulfuron (0.5 oz product) per acre. The amount of herbicide applied cannot exceed atotal of 1.0 oz chlorsulfuron (2.67 oz product) peracre and cannot exceed a total of 1.0 oz ofmetsulfuron (3.33 oz product) per acre per year (datafrom product label 2005).

Cimarron Max is a two-part product mixturemanufactured by DuPont for control of weeds andbrush on pastures, rangeland, CRP acres withestablished grasses, and noncropland. This herbicideis toxic to aquatic invertebrates and cannot be applieddirectly to water. Part A of this product contains 60%metsulfuron. Part B of this product contains 10.3%dicamba, with the acid equivalent (ae) of 1.0 lb pergallon and 29.6% 2,4-D, with the acid equivalent (ae)of 2.87 lb per gallon. A crop oil concentrate or anonionic surfactant must be used in the spray mixture. The specific application rates of this herbicide thatcontrol western snowberry have not been determinedthrough research. The label instructions and rates forcontrol or suppression of western snowberry are touse Rate I–0.15 oz metsulfuron (0.25 oz part A) and0.125 lb dicamba and 0.359 lb 2,4-D (1 pt part B) peracre. The amount of herbicide applied cannot exceeda total of 1.0 oz metsulfuron (1.67 oz part A) per acreper year (data from product label 2005).

Aliphatic Herbicides

Glyphosate is an aliphatic herbicide that isnonselective and it can kill in about 2 to 7 days from application all types of plants contacted by thechemical by inhibiting an enzyme essential for aminoacid formulation (product label 2004). Glyphosate isstrongly adsorbed to soil, so it is virtually biologicallyunavailable and immobile. The chemical is degradedby microbial activity (Hamilton et al. 2004).

Roundup is a nonselective broad spectrumsystemic herbicide manufactured by Monsanto forcontrol of annual and perennial weeds, woody brush,and trees on pastures, rangeland, CRP acres, andnoncropland. Application of this product may be asspot treatments or over-the-top wiper treatmentswhere the chemical does not come in contact with the

desirable understory vegetation. Surfactants cannotbe added to the herbicide solution when wiperapplicators are used. This herbicide cannot beapplied directly to water. This product contains41.0% glyphosate, with the acid equivalent (ae) of 3.0lb per gallon and 4.0 lb active ingredient (ai) pergallon. The specific application rates of thisherbicide that control western snowberry have notbeen determined through research. The label rates forcontrol or suppression of woody brush on grazinglandare 2.0 to 3.0 lb ai glyphosate (2 to 3 qt product) peracre. The amount of herbicide applied onto pastureand rangeland cannot exceed a total of 3.0 lb aiglyphosate (3 qt product) per acre per year (data fromproduct label 2004).

Amide Herbicides

Tebuthiuron is an amide-urea derivativeherbicide that is soil activated and absorbed by plantsthrough the roots. Tebuthiuron interferes with orinhibits the photosynthetic process, causing prematureaging and shedding of the leaves. Several leafdefoliation cycles deplete stored nonstructuralcarbohydrates and result in death of the plant(Bjerregaard et al. 1978). Tebuthiuron may persist insoils for long periods. It is adsorbed to the organicmatter and clay particles in the soil. Tebuthiuronresists photodecomposition and volatilization, and itsbreakdown by microbial activity is slow (Hamilton etal. 2004).

Spike 20P is a surface applied soil-activepelleted product manufactured by Dow AgroSciencesfor control of woody plants in rangeland, pastureland,and noncropland. This product is also available as awettable powder. This herbicide is toxic to fish andcannot be applied directly to water or to areas with ashallow water table (5 feet or less). This productcontains 20% tebuthiuron. The specific applicationrates of this herbicide that control western snowberryhave not been determined through research. Thelabel rates for control of woody brush on grazinglandare a maximum of 1.0 lb ai tebuthiuron (5 lb product)per acre in regions that receive less than 20 inchesannual precipitation and a maximum of 2.0 lb aitebuthiuron (10 lb product) per acre in regions thatreceive greater than 20 inches annual precipitation. Rates greater than 0.8 lb ai tebuthiuron (4.0 lbproduct) per acre may cause injury to perennialgrasses. The product cannot be applied to an areamore than once per year. Hay for livestock feedcannot be cut for one year after treatment. Intacttreated woody plants should not be disturbed bymowing or burning for two years after treatmentbecause the plants go through several defoliation

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cycles before stored nonstructural carbohydrates aredepleted and death occurs (data from product label 2003). At low rates of 0.25 lb ai tebuthiuron peracre, additional time for control may be required.

Period of Vulnerability

In order to kill belowground plant parts,foliage-applied herbicides must enter leaf tissuethrough the stomata openings or penetrate the cuticleon the outer layer of the leaf and then be translocateddownward through the bidirectional phloem vascularsystem to metabolically active organs of the rhizomecrown (Scifres 1980). Young leaf tissue has a thincuticle layer and the cell walls have low levels ofcellulose and lignin; this young tissue presents lowresistance to foliage-active herbicide penetration. The cuticle thickens and the cell walls stiffen asleaves mature; this aging process increases theresistance to herbicide penetration and absorption. Surfactants (or adjuvants) increase herbicidal activity. Adding surfactants to herbicide spray mixturesimproves penetration and absorption of foliage-activeherbicides into maturing leaves. The quantity ofherbicide translocated downward is related to the rateat which carbohydrates are used for plant growth(Scifres 1980) and whether the source ofcarbohydrates is derived from current photosynthateor stored reserves (Leopold and Kriedemann 1975). When the rate of photosynthesis is insufficient tomeet demands of plant growth, stored nonstructuralcarbohydrates move upward from the storage site inthe rhizome crown to the active growing points of thetwigs and leaves. When photosynthetic rates exceedplant growth demands, nonstructural carbohydratesmove downward from the leaves to the storage site inthe rhizome crown (Coyne et al. 1995). Greaterquantities of foliar-applied herbicides are translocateddownward to belowground plant parts duringreplenishment periods, when carbohydrates aremoving downward from leaves to the storage site,than during drawdown periods, when carbohydratesare moving upwards from the storage site to activelygrowing aerial parts (Adams and Bailey 1983). Changes in the amount of stored carbohydrates followa typical pattern each growing season, with periods ofdrawdown and replenishment (Coyne et al. 1995).

Adams and Bailey (1983) conducted a studyin Alberta to determine when drawdown andreplenishment periods occur in western snowberry. Rhizome crowns were collected every ten days duringthe growing season and analyzed for nonstructuralcarbohydrate content. The resulting pattern ofcarbohydrate drawdown and replenishment indicatesthe time periods and plant growth stages when foliar

application of herbicides would be expected toproduce greater kill of belowground plant parts.

The major carbohydrate drawdown periodoccurs during the rapid growth of early spring,starting in mid April and continuing until early June,shortly after full leaf stage and about the time thesucker stems have elongated to two-thirds of fulllength. Two other periods of carbohydrate drawdownoccur, one during fruit fill, from mid July to earlyAugust, and the other during fall growth, from earlySeptember to late October (Adams and Bailey 1983). Herbicides applied during the early drawdown periodwould likely penetrate the young foliage and causehigh rates of top kill (Adams and Bailey 1983). However, only small amounts of herbicide wouldreach the roots because the upward flow ofcarbohydrates during this period interferes with thedownward movement of herbicides; the result is lowlevels of kill of belowground plant parts.

The main carbohydrate replenishment periodoccurs from early June to mid July, starting during thefinal stages of sucker stem elongation and continuingthrough the flower bud stage into the early stages offlower development. A second carbohydratereplenishment period occurs between mid August andearly September (Adams and Bailey 1983). Much ofthe herbicide applied during the early replenishmentperiod would be expected to be carried downward tothe rhizome crowns, with the downward flow ofcarbohydrates moving from the leaves to thebelowground storage sites; the result would be kill ofboth aboveground and belowground plant parts(Adams and Bailey 1983). Herbicides applied duringthe earlier portions of the first replenishment periodwould possibly have greater kill levels thanherbicides applied during the latter portions becauseherbicide penetration into leaf tissue tends to decreaseas the leaves mature (Scifres 1980).

Chemical Management Research

Pelton (1953) projected that chemicalherbicide use would increase as a method to control western snowberry and indicated that 2,4-Dwas the most promising herbicide, even thoughwestern snowberry was one of the more resistantshrubs to this chemical.

McCarty (1967) conducted threeexperiments in southern Nebraska that compared one,two, or three repeated annual applications of chemicalherbicides to replicated western snowberry colonieson different dates in May, June, and July and

77

estimated percent control of aerial stems one yearafter final treatment.

McCarty (1967) considered the timeliness ofherbicide application to be important for goodwestern snowberry control. The phenological growthof western snowberry in Nebraska is similar to that ofwestern snowberry colonies across North America. Most of the growth occurs during May. New shootsare 4 to 8 inches (10-20 cm) long, with the first fourto six leaves full size in early May, and by late Maythe plants have completed full foliar development(McCarty 1967). The results of the herbicideexperiment indicated that herbicide applicationduring early to mid May was more effective forwestern snowberry aerial stem control than herbicideapplication in late May and that herbicide applicationduring late June or mid July was much less effectivethan the May applications (McCarty 1967). The Juneand July application treatments were discontinuedduring the second and third experiments.

Favorable moisture conditions and multipleretreatments appeared to improve western snowberrycontrol (McCarty 1967). Three applications of 2,4-DHV ester on the 14 and 21 May treatment dates gaveexcellent control of aerial stems (table 4). Threeapplications of 2,4-D HV ester on the late June andmid July treatment dates were much less effective ataerial stem control than the May application dates(table 4). Herbicide penetration into mature leaftissue is much less than herbicide penetration intoyoung leaf tissue (Scifres 1980). The low levels ofaerial stem control during the late June and mid Julytreatment dates may reflect low herbicide penetrationinto mature leaf tissue. The greater levels of aerialstem control during the May treatment dates mayreflect high herbicide penetration into young leaftissue.

The 2,4-D ester treatment was consistentlymore effective than the 2,4-D amine treatment on allapplication dates (table 4). The 2,4-D amine did notkill a large portion of the aerial stems. Thesesurviving stems were able to reinfest the area quicklyby respouting during subsequent growing seasons(McCarty 1967).

Two applications of 2,4-D HV ester at boththe 1.0 lb/ac and 2.0 lb/ac rates gave excellent controlof western snowberry aerial stems on all threetreatment dates in May (table 4). Percent control ofaerial stems with two applications of 2,4-D LV esterat both the 1.0 lb/ac and 2.0 lb/ac rates was onlyslightly lower than the percent control of aerial stemsfrom 2,4-D HV ester at the respective rates (table 4).

One application of 2,4-D HV ester at the 2.0lb/ac rate resulted in greater percent control of aerialstems than one application at the 1.0 lb/ac rate on allthree treatment dates in May (table 4). Treatmentswith one application of herbicide had lower percentcontrol of western snowberry aerial stems thantreatments with multiple annual applications ofherbicide.

The high percent control of aerial stemsduring the three May application dates indicates highlevels of herbicide penetration and effective top kill. However, the increase in the presence of livingwestern snowberry stems on study plots during thesecond growing season after the final treatmentindicates that only low levels of control of thebelowground plant parts had been achieved. McCarty(1967) concluded that because western snowberry canquickly reinfest an area, the use of 2,4-D everysecond or third year will be necessary for long-termpasture management.

Ferrel (1986, 1992a, 1992b) and Ferrel andWhitson (1987) conducted four experiments toevaluate various formulations of herbicides for thecontrol of western snowberry. Research wasconducted near Aladdin, Wyoming, on anunimproved pasture that had a heavy infestation ofwestern snowberry. Experimental plots of around 10by 20 ft. (3 X 6 m) were arranged in a randomizedcomplete block design with three replications. Liquidherbicide treatments were broadcast applied with aCO2 pressurized six-nozzle knapsack spray unit. Granular formulations were applied by hand. Percentcontrol of aerial stems was evaluated by visualestimates one year following treatment (Ferrel 1986,1992a, 1992b; Ferrel and Whitson 1987).

The phenological growth of westernsnowberry in Wyoming is similar to that of westernsnowberry colonies across North America. Most ofthe growth occurs during May, and by late May thestems are 6 to 20 inches (15-51 cm) tall and near fullleaf development. Stems are at full leaf stage and 12to 20 inches (31-52 cm) tall in early June and at budto full bloom growth stages and 12 to 20 inches (31-51 cm) tall in early July. In mid September, stems are15 to 36 inches (38-91 cm) tall, and leaves arebeginning to drop (Ferrel 1986, 1992a, 1992b; Ferreland Whitson 1987).

The objective of these four experiments wasto perform a rapid screening of herbicides andidentify chemicals that showed promise for thecontrol of western snowberry. Most of the chemicals

78

or chemical mixtures were evaluated at more than oneapplication rate.

Spring application of triclopyr, fluroxypyr,fluroxypyr + triclopyr, tebuthiuron, and fosamine at6.0 lb ai/ac, and summer application of triclopyr,Dowco 290 + 2,4-D A, Dowco 290 + picloram,metsulfuron, and metsulfuron + 2,4-D LVE did notshow promise for controlling western snowberryaerial stems at the rates and application datesevaluated (table 5). Spring application of 2,4-D LVEand summer application of picloram provided 70%and 73% control of aerial stems at 2.0 lb ai/ac,respectively (table 5). Spring application of fosamineat 12.0 lb and 24.0 lb ai/ac, and glyphosate at 1.125lb ai/ac provided 82%, 96%, and 95% control ofaerial stems, respectively (table 5). Springapplication of chlorsulfuron, metsulfuron, andmetsulfuron + 2,4-D LVE provided 100% control ofaerial stems at the rates evaluated, respectively (table5), and showed considerable promise for westernsnowberry control.

Experiment #4 evaluated two herbicideapplication dates; one date was successful, and theother date was not successful. The differences in thepercent control of western snowberry aerial stemsbetween the two herbicide application dates are mostlikely related to differences in the quantities ofherbicide penetration into the leaves and differencesin the quantities of herbicide translocated tobelowground plant parts. Greater quantities ofherbicide penetrate young leaves than penetratemature leaves, and greater quantities of foliar-appliedherbicide are translocated downward duringcarbohydrate replenishment periods than duringdrawdown periods. On the early June applicationdate, western snowberry has fully developed youngleaves and is just starting the first carbohydratereplenishment period. On the mid Septemberapplication date, western snowberry has matureleaves near senescence and is in a late seasoncarbohydrate drawdown period. The early Juneherbicide application date resulted in 100% control ofaerial stems, and the mid September application dateresulted in 50% control of aerial stems one year aftertreatment (table 5).

Bowes (1991) conducted two chemicalmanagement experiments northeast of Regina,Saskatchewan, to evaluate the effects of herbicidemixtures on reducing western snowberry regrowthsuckers in the aspen parkland vegetation zonefollowing bulldozer treatments that sheared aspenpoplar trees at the surface of frozen soil. Herbicidetreatments of dicamba plus 2,4-D LVE (ester) and

plus 2,4-D A (amine) applied at the rates of 1.34 +1.96 lb ai/acre (1.5 + 2.2 kg/ha) in experiment #1 and1.34 + 1.78 lb ai/acre (1.5 + 2.0 kg/ha) in experiment#2 were applied with a hand-held compressed-airsprayer one, two, and three times every year or every-other-year on 6 June 1981, 16 June 1982, and 16 June1983 in experiment #1 and on 16 June 1983, 19 June1984, and 27 June 1985 in experiment #2. The studyanalyzed data for percent canopy cover of westernsnowberry collected during mid August for nine yearsand data for aboveground herbage biomass of grassesand forbs collected during late June to mid July foreight years from plots replicated four times.

Bowes (1991) considered western snowberryeffectively controlled when the canopy cover wasreduced to less than 1%. Herbicide mixtures ofdicamba + 2,4-D LVE and dicamba + 2,4-D A hadsimilar effects in reducing canopy cover of westernsnowberry (Bowes 1991); however, sucker regrowthwas greater five years after final treatment on thedicamba + 2,4-D A plots than on the dicamba + 2,4-DLVE plots (table 6). Dicamba + 2,4-D LVE anddicamba + 2,4-D A applied two and three timesduring early to mid June were more effective atreducing western snowberry canopy cover thandicamba + 2,4-D LVE and dicamba + 2,4-D Aapplied one time during early June (table 6). Nodifferences in canopy cover one year or five yearsafter final treatment were found between treatmentswith herbicide mixtures applied two times every yearor every-other-year (table 6). Dicamba + 2,4-D LVEapplied two times during mid to late June was moreeffective than dicamba + 2,4-D LVE applied twotimes during early to mid June (table 6). Dicamba +2,4-D LVE applied one time during mid June wasmore effective than dicamba + 2,4-D LVE appliedone time during early June (table 6).

Grass biomass production was greater on theherbicide treated plots than on the untreated controlplots (Bowes 1991) (table 7). Herbicide mixtures ofdicamba + 2,4-D LVE and dicamba + 2,4-D A hadsimilar effects on grass biomass production; however,five years after final treatment, grass biomassproduction was greater on the dicamba + 2,4-D LVEplots than on the dicamba + 2,4-D A plots (table 7). Dicamba + 2,4-D LVE and dicamba + 2,4-D Aapplied two and three times were more effective atincreasing grass biomass production than dicamba +2,4-D LVE and dicamba + 2,4-D A applied one time(table 7). No differences in grass biomass productionone year or five years after final treatment were foundbetween treatments with herbicide mixtures appliedtwo times every year or every-other-year (table 7). Dicamba + 2,4-D LVE applied two times during mid

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to late June was more effective at increasing grassbiomass production than dicamba + 2,4-D LVEapplied two times during early to mid June (table 7).

Both dicamba + 2,4-D LVE and dicamba +2,4-D A herbicide mixtures reduced forb biomassproduction. Two and three applications of theherbicide mixtures reduced forb biomass productionmore than a single application of the herbicidemixtures (Bowes 1991).

Western snowberry was not completelyeradicated by the herbicide mixtures of dicamba and2,4-D tested (Bowes 1991). Dicamba + 2,4-D LVEand dicamba + 2,4-D A have similar effects onwestern snowberry canopy cover and grass and forbherbage biomass production one year after finaltreatment; however, five years after final treatment,the effects from dicamba + 2,4-D A had diminishedfurther than those from dicamba + 2,4-D LVE. Twoand three applications of herbicide mixtures are moreeffective than a single application. Multipleapplications every year or every-other-year havesimilar effects following the final treatment. Herbicide mixtures applied during mid to late Juneare more effective than mixtures applied during earlyto mid June.

Bowes and Spurr (1995) conducted twochemical management experiments southeast ofRegina, Saskatchewan, to evaluate the effects fromherbicide treatments on reducing western snowberryin mixed grass prairie that had not been grazed for tenyears. Single herbicide treatments of metsulfuron,metsulfuron + 2,4-D LVE (ester), and 2,4-D LVEalone were applied with a hand-held compressed-airsprayer when western snowberry sucker stems were ator near full expansion growth stage on 16 June 1986in experiment #1 and on 12 June 1987 in experiment#2. The study analyzed data for percent canopy coverof western snowberry collected during mid August forsix years and data for aboveground biomass ofwestern snowberry aerial stems and abovegroundherbage biomass of grasses collected between midJune and mid July each year of the study from plotsreplicated four times.

Bowes (1991) considered western snowberryeffectively controlled when the canopy cover wasreduced to less than 1%. All herbicide treatmentsapplied 16 June in experiment #1 and all treatmentsapplied 12 June in experiment #2, with the exceptionof one treatment, resulted in 95% or better reductionof western snowberry canopy cover during the year oftreatment. The low rate with 0.04 oz/acre (3 g/ha) ofmetsulfuron + 2,4-D LVE treatment in experiment #2

resulted in only 85% reduction in canopy cover (table8).

All herbicide treatments applied 16 June inexperiment #1, with the exception of one treatment,resulted in 95% or better reduction of canopy coverfive years after treatment. The 2,4-D LVE alonetreatment resulted in only 86% reduction in canopycover five years after treatment (table 8). Twotreatments applied 12 June in experiment #2 resultedin 95% or better reduction of canopy cover five yearsafter treatment. The treatments with the 0.21 oz/acre(15 g/ha) rate of metsulfuron alone and the 0.21oz/acre (15 g/ha) rate of metsulfuron + 2,4-D LVEresulted in 95% or better reduction in canopy coverfive years after treatment (table 8). The treatmentswith lower rates of 0.11, 0.07, and 0.04 oz/acre (7.5,5, and 3 g/ha) metsulfuron alone and metsulfuron +2,4-D LVE, and with 2,4-D LVE alone applied 12June in experiment #2 resulted in western snowberry canopy cover reductions of less than 95% five yearsafter treatment (table 8). Percent canopy coverreductions were similar among the high rates of 0.21,0.43, and 0.86 oz/acre (15, 30, and 60 g/ha)metsulfuron alone and metsulfuron + 2,4-D LVE oneyear and five years after treatment. Metsulfuronapplied at the 0.43 and 0.86 oz/acre (30 and 60 g/ha)rates was no more effective than metsulfuron appliedat the 0.21 oz/acre (15 g/ha) rate.

All herbicide treatments applied 16 June inexperiment #1 resulted in 95% or better reduction ofwestern snowberry aboveground biomass one yearafter treatment (table 9). All treatments applied 12June in experiment #2, with the exception of twotreatments, resulted in 95% or better reduction ofwestern snowberry aboveground biomass one yearafter treatment. The treatments with the low rate of0.04 oz/acre (3 g/ha) metsulfuron + 2,4-D LVE andwith 2,4-D LVE alone resulted in aerial stem biomassreductions of less than 95% one year after treatment(table 9).

All herbicide treatments applied 16 June inexperiment #1, with the exception of one treatment,resulted in 95% or better reduction of westernsnowberry aerial stem biomass five years after treatment. The 2,4-D LVE alone treatment resultedin aerial stem biomass reduction of only 89% fiveyears after treatment (table 9). Two treatmentsapplied 12 June in experiment #2 resulted in highreductions of aerial stem biomass five years aftertreatment. These two treatments were the 0.21oz/acre (15 g/ha) rate of metsulfuron alone and the0.21 oz/acre (15 g/ha) rate of metsulfuron + 2,4-DLVE (table 9). The herbicide treatments with the low

80

rates of 0.04, 0.07, and 0.11 oz/acre (3, 5, and 7.5g/ha) metsulfuron alone and metsulfuron + 2,4-DLVE, and with 2,4-D LVE alone applied 12 June inexperiment #2 had considerable western snowberryaerial stem biomass production from regrowth ofrhizome suckers, crown suckers, and new growth onexisting stems five years after treatment, and thesetreatments were considered not to be successful long-term control of western snowberry (Bowes and Spurr1995).

All treatments with herbicide applied 16June in experiment #1 had greater grass productionthan the untreated control plots one year and fiveyears after treatment (table 10). Grass biomassproduction on the treatments with herbicide applied12 June in experiment #2 was not much differentfrom grass production on the untreated control plotsone year after treatment. However, all treatmentswith herbicide applied 12 June in experiment #2 hadgreater grass production than the untreated controlplots five years after treatment (table 10). Reductionof western snowberry canopy cover resulted ingreater quantities of sunlight reaching the herbaceouslayer and caused an increase in grass herbage biomassproduction.

The time of herbicide application isimportant (Bowes and Spurr 1995). Foliar-appliedherbicides are translocated through the phloemvascular system when materials are movingdownward. The carbohydrate reserves in the crownsof western snowberry are drawn down during therapid growth of early spring and are at the lowestlevel about the time the sucker stems have elongatedto two-thirds of full length, during the ten days priorto 9 June (Adams and Bailey 1983). From early Juneto mid July, the energy reserves in the crowns arereplenished with surplus carbohydrates produced inthe leaves and moved down into belowground plantparts. That the herbicide treatments applied 16 Junewere more effective than the treatments applied 12June indicates that greater quantities of herbicidewere translocated to the crowns on the laterapplication date.

Western snowberry was not eradicated bythe metsulfuron and 2,4-D treatments tested (Bowesand Spurr 1995). Metsulfuron was more effective atkilling western snowberry crowns than 2,4-D becausea greater percent of the metsulfuron than of the 2,4-Dwas translocated through the phloem (Bowes andSpurr 1995). The addition of 2,4-D to metsulfurondid not improve the effectiveness. At the lowchemical rates, metsulfuron was more effective alonethan when 2,4-D was present in the mixture. Bowes

and Spurr (1995) concluded that the effectiveherbicide treatment for the control of westernsnowberry through the fifth year after treatment wasmetsulfuron applied alone at the rate of 0.21 ozai/acre (15 g/ha) during mid June.

Bowes and Spurr (1996) conducted twochemical management experiments northeast ofRegina, Saskatchewan, to evaluate the effects ofherbicide treatments on reducing western snowberryregrowth suckers in the aspen parkland vegetationzone following bulldozer treatments that shearedaspen poplar trees at the surface of frozen soil. Single herbicide treatments of metsulfuron,metsulfuron + 2,4-D LVE (ester), and 2,4-D LVEalone were applied with a hand-held compressed-airsprayer on 19 June 1985 in experiment #1 and on 10June 1986 in experiment #2. The study analyzed datafor percent canopy cover of western snowberrycollected during mid August for seven years and datafor aboveground herbage biomass of grasses andforbs collected during late June to mid July for fiveyears from plots replicated four times.

All herbicide treatments applied 19 June inexperiment #1 and 10 June in experiment #2 reducedwestern snowberry canopy cover to less than 1%during the year of treatment (table 11). Bowes (1991)considered western snowberry effectively controlledwhen the canopy cover was reduced to less than 1%. Percent canopy cover changed very little on theuntreated and treated areas of both experiments sixyears after treatment (Bowes and Spurr 1996).

All treatments with herbicide applied 19June in experiment #1 and 10 June in experiment #2had greater five year mean grass biomass productionthan the untreated controls (table 12). Treatmentswith metsulfuron applied at 0.21, 0.43, and 0.86oz/acre (15, 30, and 60 g/ha) rates on 19 June inexperiment #1 and 10 June in experiment #2 hadlower five year mean forb biomass production thanthe untreated controls. The addition of 2,4-D LVE tometsulfuron resulted in greater reductions in the fiveyear mean forb biomass production for the three ratesof metsulfuron, respectively (table 12). Treatmentswith application of 2,4-D LVE alone on 19 June inexperiment #1 had greater five year mean forbbiomass production than the untreated controls. Treatments with application of 2,4-D LVE alone on10 June in experiment #2 had lower five year meanforb biomass production than the untreated controls(table 12).

Western snowberry was not completelyeradicated by the metsulfuron and 2,4-D LVE

81

treatments tested (Bowes and Spurr 1996). Metsulfuron applied at the high rates of 0.21, 0.43,and 0.86 oz/acre (15, 30, and 60 g/ha) effectivelykilled western snowberry crowns and controlledrhizome sucker canopy cover at less than 1% sixyears after treatment. Application of 2,4-D LVEalone at the 1.78 lb/acre (2 kg/ha) rate effectivelykilled western snowberry and controlled canopycover at 1% six years after treatment. The addition of2,4-D LVE to metsulfuron did not improve theeffectiveness. Differences from the application dateswere not found between respective herbicidetreatments of metsulfuron and metsulfuron + 2,4-DLVE. Metsulfuron applied at 0.43 and 0.86 oz/acre(30 and 60 g/ha) was no more effective than the 0.21oz/acre (15 g/ha) rate. Metsulfuron applied alone atthe rate of 0.21 oz/acre (15 g/ha) during mid June isan effective herbicide treatment for the control ofwestern snowberry.

Management Implications

Successful chemical management of westernsnowberry depends on terminating the regenerativecapabilities of the rhizomes and the cluster of stembases on the crowns. Two critical factors must occurin order for sufficient quantities of foliage-activeherbicides to reach the site of activity in thebelowground plant parts and interfere with theirrespective specific physiological processes. First, theherbicides must enter the leaf tissue through thestomata openings or penetrate the outer cuticle layer,be absorbed through leaf tissue by diffusion, and bemoved to the vascular system within the leaf. Second, the herbicides must be translocated from theleaves downward though the phloem vascular systemto the metabolically active sites of the crowns andrhizomes. The vulnerable stage when the leaf tissueabsorbs herbicides and the phloem systemtranslocates herbicides downward is remarkablynarrow, during mid June.

Spring growth of western snowberry starts inmid to late April, with rapid twig elongation and leafgrowth and expansion occurring simultaneously untillate May or early June, when the appearance offlower buds at the twig tips ends both rapid twiggrowth and the possibility for additional new leaves. Nonstructural carbohydrates move from the storagesite in the rhizomes and the crowns upward throughthe phloem vascular system to the active growingpoints during the spring growth period of mid Aprilto early June. By early June, the twigs havecompleted about 75% of their growth and the leavesare near full expansion. Herbicides can readilypenetrate young western snowberry leaves during

May and early June. However, when westernsnowberry colonies are at that stage of growth,carbohydrate movement upward through the phloemprevents downward movement of herbicides. Thetwigs continue to grow at a slower rate, and by midJune the twigs have reached about 95% of theirannual growth. Sometime between early June andmid June, processes within the plant shift from usingstored carbohydrates at the growing points to usingthe carbohydrates produced by leaf photosynthesis. As the rate of growth slows and leaf photosynthesisincreases, a surplus of carbohydrates is produced andmust be moved downward through the phloem forstorage in the rhizomes and crowns. This change indirection of carbohydrate flow permits thetranslocation of herbicides from the leaves downwardto the belowground plant parts. Meanwhile,maturation of the leaves has been continuing withdevelopment of a thicker cuticle layer and denser cellwalls; the result is an increasing resistance toherbicide penetration and absorption. The twocritical factors required for successful chemicalmanagement of western snowberry occurcoincidentally during only a brief vulnerable stage,from about 10 June until 20 June, when herbicidepenetration into leaf tissue is decreasing andherbicide translocation downward is increasing. Greater quantities of herbicide are translocateddownward during mid to late June than during earlyto mid June. Leaf penetration by herbicides isimproved with wetting agents, and these surfactantsshould be added to all foliage-active herbicide spraymixtures.

Soil-active herbicides have a relatively widewindow of opportunity for treatment and require onlythat application be ahead of a rainy period. Theherbicides move into the roots anytime the roots areabsorbing water. Movement upward in the xylemvascular system is not as complex as movementwithin the phloem system. Plants have few resistancemechanisms to restrict activity of soil-appliedherbicides. Usually lower rates are quite effective,but a longer period of time may be required toproduce the desired results.

Comparisons and evaluations of theherbicide costs for chemical management of westernsnowberry should include the treatment cost per acreand the frequency of retreatment. None of theherbicides approved for control of woody plants ongrazingland are known to eradicate westernsnowberry from grassland ecosystems. Retreatmentwill be required. Unfortunately, the frequency rate ofretreatment for the various herbicides is currently notknown.

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Acknowledgment

I am grateful to Sheri Schneider forassistance in production of this manuscript and fordevelopment of the tables. I am grateful to Amy M.Kraus for assistance in preparation of this manuscript.

Table 4. Percent reduction of western snowberry live aerial stems from chemical herbicides estimated one year after final treatment.

Number of Repeated AnnualApplications

Treatment Dates

Ratelbs ai/ac

12-15May

19-22May

26-29May

28Jun

16Jul

3 Applications

2,4-D HVE na 97 96 82 65 26

2,4-D A na 65 61 45 45 20

2 Applications

2,4-D HVE 1.0 lb 99 100 99

2,4-D HVE 2.0 lb 100 100 100

2,4-D LVE 1.0 lb 90 92 87

2,4-D LVE 2.0 lb 94 97 85

1 Application

2,4-D HVE 1.0 lb 62 24 84

2,4-D HVE 2.0 lb 87 71 85

Data from McCarty 1967

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Table 5. Percent control of western snowberry live aerial stems from chemical herbicides estimated visually one year following final treatment.

HerbicideTreatment

% Aerial Stem Control

Spring Application Summer Application

Experiment #1, 4 Jul 84

Triclopyr

1.0 lb ai/ac 0

2.0 lb ai/ac 0

Dowco 290 + 2,4-D A

0.25 + 1.0 lb ai/ac 10

0.38 +1.5 lb ai/ac 20

Dowco 290 + picloram

0.25 + 2.25 lb ai/ac 20

Picloram

2.0 lb ai/ac 73

Experiment #2, 30 May 85

Triclopyr

1.0 lb ai/ac 0

2.0 lb ai/ac 0

Fluroxypyr

2.0 lb ai/ac 0

3.0 lb ai/ac 0

Fluroxypyr + Triclopyr

1.0 + 1.0 lb ai/ac 0

1.5 + 1.5 lb ai/ac 0

Tebuthiuron

0.25 lb ai/ac 0

0.50 lb ai/ac 0

0.75 lb ai/ac 0

1.0 lb ai/ac 0

2,4-D LVE

2.0 lb ai/ac 70

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Table 5. (Cont.). Percent control of western snowberry live aerial stems from chemical herbicides estimated visually one year following final treatment.

HerbicideTreatment

% Aerial Stem Control

Spring Application Summer Application

Experiment #3, 7 Jun 89

Glyphosate

1.125 lb ai/ac 95

Fosamine

6.0 lb ai/ac 13

12.0 lb ai/ac 82

24.0 lb ai/ac 96

Metsulfuron

0.3 oz ai/ac 100

0.6 oz ai/ac 100

1.2 oz ai/ac 100

Chlorsulfuron

0.4 oz ai/ac 100

0.8 oz ai/ac 100

2.2 oz ai/ac 100

Experiment #4, 7 Jun 90, 13 Sep 90

Metsulfuron

0.2 oz ai/ac 100 50

0.3 oz ai/ac 100 50

0.4 oz ai/ac 100 50

Metsulfuron + 2,4-D LVE

0.2 oz + 1.0 lb ai/ac 100 50

0.3 oz + 1.0 lb ai/ac 100 50

0.4 oz + 1.0 lb ai/ac 100 50

Data from Ferrell 1986, 1992a, 1992b, and Ferrell and Whitson 1987

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Table 6. Percent canopy cover of western snowberry and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after final treatment.

one yearafter final treatment

five yearsafter final treatment

Herbicide Treatmentcanopy cover

%% change

from controlcanopy cover

%% change

from control

Experiment #1, 1981-1989

No Herbicide

Control 6 6

Dicamba + 2,4-D LVE 1.34 + 1.96 lb ai/ac

3 applications 6 Jun 81, 16 Jun 82, 16 Jun 83 0 -100.0 <1 >-83.3

2 applications 6 Jun 81, 16 Jun 82 <1 >-83.3 1 -83.3

6 Jun 81, 16 Jun 83 <1 >-83.3 <1 >-83.3

1 application 6 Jun 81 2 -66.7 5 -16.7

Dicamba + 2,4-D A 1.34 + 1.96 lb ai/ac

3 applications 6 Jun 81, 16 Jun 82, 16 Jun 83 <1 >-83.3 2 -66.7

2 applications 6 Jun 81, 16 Jun 82 <1 >-83.3 3 -50.0

6 Jun 81, 16 Jun 83 <1 >-83.3 3 -50.0

1 application 6 Jun 81 2 -66.7 6 0.0

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Table 6. (Cont.). Percent canopy cover of western snowberry and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after final treatment.



Herbicide Treatmentcanopy cover

%% change

from controlcanopy cover

%% change

from control


No herbicide

Control 3 3


2 applications 16 Jun 83, 19 Jun 84 0 -100.0 <1 >-66.7

16 Jun 83, 27 Jun 85 0 -100.0 <1 >-66.7

1 application 16 Jun 83 0 -100.0 1 -66.7

Data from Bowes 1991

87

Table 7. Grass biomass production and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after final treatment.



Herbicide TreatmentGrass Biomass

Productionlbs/ac

% changefrom control

Grass BiomassProduction

lbs/ac



No Herbicide

Control 276.52 276.52


3 applications 6 Jun 81, 16 Jun 82, 16 Jun 83 1195.28 332.3 927.68 235.5

2 applications 6 Jun 81, 16 Jun 82 1079.32 290.3 749.28 171.0

6 Jun 81, 16 Jun 83 1141.76 312.9 749.28 171.0

1 application 6 Jun 81 838.48 203.2 526.28 90.3

Dicamba + 2,4-D A 1.34 + 1.96 lb ai/ac

3 applications 6 Jun 81, 16 Jun 82, 16 Jun 83 1266.64 358.1 695.76 151.6


6 Jun 81, 16 Jun 83 1239.88 348.4 660.08 138.7

1 application 6 Jun 81 544.12 96.8 517.36 87.1

88

Table 7. (Cont.). Grass biomass production and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after final treatment.



Herbicide TreatmentGrass Biomass

Productionlbs/ac



lbs/ac



No herbicide

Control 338.96 338.96



16 Jun 83, 27 Jun 85 1257.72 271.1 1382.60 307.9

1 application 16 Jun 83 722.52 113.2 660.08 94.7

Data from Bowes 1991

89

Table 8. Percent canopy cover of western snowberry and percent change from control treatment resulting from herbicide treatments evaluated two months and five years after treatment.

two monthsafter treatment

five yearsafter treatment

Herbicide TreatmentCanopy cover

%% change

from controlCanopy cover

%% change

from control

Experiment #1, 1986-1989 16 June 1986

No Herbicide

Control 32.1 72.2

Metsulfuron

0.11 oz/ac 0.1 -99.7 0.7 -99.0

0.21 oz/ac <0.1 >-99.7 <0.1 >-99.9

0.43 oz/ac <0.1 >-99.7 0.5 -99.3

0.86 oz/ac <0.1 >-99.7 <0.1 >-99.9


0.11 oz/ac +1.78 lb/ac <0.1 >-99.7 0.5 -99.3

0.21 oz/ac +1.78 lb/ac <0.1 >-99.7 0.4 -99.4

0.43 oz/ac +1.78 lb/ac <0.1 >-99.7 0.3 -99.6

0.86 oz/ac +1.78 lb/ac <0.1 >-99.7 <0.1 >-99.9

2,4-D LVE 1.78 lb/ac 1.1 -96.6 9.0 -87.5

90

Table 8. (Cont.). Percent canopy cover of western snowberry and percent change from control treatment resulting from herbicide treatments evaluated two months and five years after treatment.




%% change


%% change

from control

Experiment #2, 1987-1992 12 June 1987

No Herbicide

Control 32.2 76.4

Metsulfuron

0.04 oz/ac 0.2 -99.4 19.9 -74.0

0.07 oz/ac 0.2 -99.4 7.6 -90.1

0.11 oz/ac <0.1 >-99.7 8.1 -89.4

0.21 oz/ac <0.1 >-99.7 2.1 -97.3


0.04 oz/ac +1.78 lb/ac 4.8 -85.1 31.3 -59.0

0.07 oz/ac +1.78 lb/ac 1.1 -96.6 7.9 -89.7

0.11 oz/ac +1.78 lb/ac 0.1 -99.7 4.7 -93.8

0.21 oz/ac +1.78 lb/ac 0.1 -99.7 0.3 -99.6

2,4-D LVE 1.78 lb/ac 0.3 -99.1 49.1 -35.7

Data from Bowes and Spurr 1995

91

Table 9. Western snowberry aboveground biomass and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after treatment.

one yearafter treatment


Herbicide Treatment

Westernsnowberry

abovegroundbiomasslbs/ac


Westernsnowberry



Experiment #1, 1986-1989 16 June 1986

No Herbicide

Control 1873.11 2470.48

Metsulfuron

0.11 oz/ac 0.09 -99.9 <0.09 >-99.9

0.21 oz/ac <0.09 >-99.9 <0.09 >-99.9

0.43 oz/ac <0.09 >-99.9 <0.09 >-99.9

0.86 oz/ac <0.09 >-99.9 <0.09 >-99.9


0.11 oz/ac +1.78 lb/ac <0.09 >-99.9 <0.09 >-99.9

0.21 oz/ac +1.78 lb/ac 0.09 -99.9 19.09 -99.2

0.43 oz/ac +1.78 lb/ac 3.03 -99.8 1.34 -99.9

0.86 oz/ac +1.78 lb/ac 3.03 -99.8 <0.09 >-99.9

2,4-D LVE 1.78 lb/ac 2.23 -99.9 267.60 -89.2

92

Table 9. (Cont.). Western snowberry aboveground biomass and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after treatment.



Herbicide Treatment

Westernsnowberry



Westernsnowberry



Experiment #2, 1987-1992 12 June 1987

No Herbicide

Control 1071.02 3597.44

Metsulfuron

0.04 oz/ac 50.13 -95.3 354.03 -90.2

0.07 oz/ac 6.33 -99.4 125.06 -96.5

0.11 oz/ac 21.76 -98.0 349.84 -90.3

0.21 oz/ac 1.34 -99.9 20.43 -99.4


0.04 oz/ac +1.78 lb/ac 99.01 -90.8 794.95 -77.9

0.07 oz/ac +1.78 lb/ac 44.96 -95.8 281.34 -92.2

0.11 oz/ac +1.78 lb/ac 3.84 -99.6 222.02 -93.8

0.21 oz/ac +1.78 lb/ac 3.84 -99.6 8.83 -99.8

2,4-D LVE 1.78 lb/ac 260.55 -75.7 1672.59 -53.5


93

Table 10. Grass biomass production and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after treatment.



Herbicide Treatment


lbs/ac



lbs/ac


Experiment #1, 1986-1989 16 June 1986

No Herbicide

Control 359.48 643.13

Metsulfuron

0.04 oz/ac 759.98 +111.4 1740.29 +170.6

0.07 oz/ac 536.98 +49.4 1486.07 +131.1

0.11 oz/ac 591.40 +64.5 1567.24 +143.7

0.21 oz/ac 733.22 +104.0 1744.75 +171.3


0.04 oz/ac +1.78 lb/ac 753.74 +109.7 1581.52 +145.9

0.07 oz/ac +1.78 lb/ac 732.33 +103.7 1659.12 +158.0

0.11 oz/ac +1.78 lb/ac 619.05 +72.2 1660.90 +158.3

0.21 oz/ac +1.78 lb/ac 759.98 +111.4 1424.52 +121.5

2,4-D LVE 1.78 lb/ac 765.34 +112.9 1678.74 +161.0

94

Table 10. (Cont.). Grass biomass production and percent change from control treatment resulting from herbicide treatments evaluated one year and five years after treatment.



Herbicide Treatment


lbs/ac% change

from control


lbs/ac% change

from control

Experiment #2, 1987-1992 12 June 1987

No Herbicide

Control 317.55 1577.06

Metsulfuron

0.04 oz/ac 397.83 +25.3 2580.56 +63.6

0.07 oz/ac 424.59 +33.7 2370.04 +50.3

0.11 oz/ac 340.74 +7.3 2630.51 +66.8

0.21 oz/ac 333.61 +5.1 2567.18 +62.8


0.04 oz/ac +1.78 lb/ac 322.01 +1.4 2231.78 +41.5

0.07 oz/ac +1.78 lb/ac 302.39 -4.8 2799.99 +77.5

0.11 oz/ac +1.78 lb/ac 382.67 +20.5 2180.05 +38.2

0.21 oz/ac +1.78 lb/ac 390.70 +23.0 2326.34 +47.5

2,4-D LVE 1.78 lb/ac 338.07 +6.5 2167.56 +37.4


95

Table 11. Percent canopy cover of western snowberry and percent change from control treatment resulting from herbicide treatments evaluated two months and six years after treatment.


six yearsafter treatment


%% change


%% change

from control

Experiment #1, 1985-1991 19 June 1985

No Herbicide

Control 9 9

Metsulfuron

0.21 oz/ac <1 >-88.9 2 -77.8

0.43 oz/ac <1 >-88.9 <1 >-88.9

0.86 oz/ac <1 >-88.9 <1 >-88.9


0.21 oz/ac +1.78 lb/ac <1 >-88.9 <1 >-88.9

0.43 oz/ac +1.78 lb/ac <1 >-88.9 <1 >-88.9

0.86 oz/ac +1.78 lb/ac <1 >-88.9 <1 >-88.9

2,4-D LVE 1.78 lb/ac <1 >-88.9 1 -88.9

Experiment #2, 1986-1992 10 June 1986

No Herbicide

Control 8 8

Metsulfuron

0.21 oz/ac <1 >-87.5 <1 >-87.5

0.43 oz/ac <1 >-87.5 <1 >-87.5

0.86 oz/ac <1 >-87.5 <1 >-87.5


0.21 oz/ac +1.78 lb/ac <1 >-87.5 <1 >-87.5

0.43 oz/ac +1.78 lb/ac <1 >-87.5 1 -87.5

0.86 oz/ac +1.78 lb/ac <1 >-87.5 1 -87.5

2,4-D LVE 1.78 lb/ac <1 >-87.5 1 -87.5


96

Table 12. Grass and forb biomass production and percent change from control treatment resulting from herbicide treatments evaluated as five year means.

Five year mean Five year mean

Herbicide Treatment


lbs/ac


Forb BiomassProduction

lbs/ac


Experiment #1, 1985-1991 19 June 1985

No Herbicide

Control 634.21 245.30

Metsulfuron

0.21 oz/ac 966.93 +52.5 227.46 -7.3

0.43 oz/ac 1342.46 +111.7 110.61 -54.9

0.86 oz/ac 1400.44 +120.8 33.00 -86.5


0.21 oz/ac +1.78 lb/ac 1089.13 +71.7 92.77 -62.2

0.43 oz/ac +1.78 lb/ac 1144.44 +80.5 37.46 -84.7

0.86 oz/ac +1.78 lb/ac 1377.25 +117.2 29.44 -88.0

2,4-D LVE 1.78 lb/ac 891.11 +40.5 298.82 +21.8

Experiment #2, 1986-1992 10 June 1986

No Herbicide

Control 379.99 565.53

Metsulfuron

0.21 oz/ac 1012.42 +166.4 225.68 -60.1

0.43 oz/ac 940.17 +147.4 279.20 -50.6

0.86 oz/ac 1263.96 +232.6 190.00 -66.4


0.21 oz/ac +1.78 lb/ac 1286.26 +238.5 198.92 -64.8

0.43 oz/ac +1.78 lb/ac 1129.27 +197.2 148.96 -73.7

0.86 oz/ac +1.78 lb/ac 1275.56 +235.7 151.64 -73.2

2,4-D LVE 1.78 lb/ac 758.20 +99.5 460.27 -18.6


97

Literature Cited

Adams, B.W., and A.W. Bailey. 1983. Effect ofmowing on energy reserves of westernsnowberry. Agriculture and ForestryBulletin (Special Issue). p. 72-75.

Bjerregaard, R.S., J.A. Keaton, K.E. McNeill, andL.C. Warner. 1978. Rangeland brush andweed control with tebuthiuron. Proceedings,First Rangeland Congress. p. 654-656.

Bowes, G.G. 1991. Long-term control of aspenpoplar and western snowberry with dicambaand 2,4-D. Canadian Journal of PlantScience 71:1121-1131.

Bowes, G.G., and D.T. Spurr. 1995. Improvedforage production following westernsnowberry (Symphoricarpos occidentalisHook.) control with metsulfuron methyl. Canadian Journal of Plant Science 75:935-940.

Bowes, G.G., and D.T. Spurr. 1996. Control ofaspen poplar, balsam poplar, prickly rose,and western snowberry with metsulfuron-methyl and 2,4-D. Canadian Journal ofPlant Science 76:885-889.

Coyne, P.I., M.J. Trlica, and C.E. Owensby. 1995. Carbon and nitrogen dynamics in rangeplants. p. 59-167. in D.J. Bedunah and R.E.Sosebee (eds.). Wildland plants:physiological ecology and developmentalmorphology. Society for RangeManagement, Denver, CO.

Ferrell, M.A. 1986. Evaluation of herbicides forcontrol of western snowberry. WesternSociety of Weed Science-Research ProgressReport. p. 38.

Ferrell, M.A. 1992a. Control of western snowberry (Symphoricarpos occidentalis Hook.) withvarious herbicides. Western Society ofWeed Science-Research Progress Report. p. I-75.

Ferrell, M.A. 1992b. Control of western snowberry (Symphoricarpos occidentalis Hook.) withmetsulfuron. Western Society of WeedScience-Research Progress Report. p. I-76.

Ferrell, M.A., and T.D. Whitson. 1987. Herbicidecontrol evaluations on western snowberry. Western Society of Weed Science-ResearchProgress Report. p. 53.

Hamilton, W.T., A. McGinty, D.N. Ueckert, C.W.Hanselka, and M.R. Lee. 2004. Brushmanagement, past, present, future. Texas A& M University Press, College Station, TX.

Herbicide Product Labels. Crop Data ManagementSystems. http://www.cdms.net/manuf/manuf.asp.

Leopold, A.C., and P.E. Kriedemann. 1975. Plantgrowth and development. McGraw-HillBook Co., New York, NY.

Material Safety Data Sheets. Crop DataManagement Systems. http://www.cdms.net/manuf/manuf.asp.

McCarty, M.K. 1967. Control of westernsnowberry in Nebraska. Weeds 15:130-133.

Pelton, J. 1953. Studies on the life-history of Symphoricarpos occidentalis Hook., inMinnesota. Ecological Monographs 23:17-39.

Scifres, C.J. 1980. Brush management, principlesand practices for Texas and the Southwest. Texas A & M University Press, CollegeStation, TX.

98

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chemical management of western snowberry · 6/12/1987 · chemical management with herbicide...

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